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Missions to Mars - Spirit and Opportunity

The Mars Exploration Rovers consists of twin probes that are controllable rovers that move freely on the surface of Mars.

The rovers are:

  • Spirit (MER-A)
  • Opportunity (MER-B)

Spirit was launched on June 10, 2003 at 1:58 PM EST (Pad 17-A) and landed on Mars on January 3, 2004. The Spirit rover carries a memorial plaque dedicated to the crew of the Space Shuttle Columbia - the loss of the Space Shuttle on February 2, 1003.

Opportunity was launched on July 7, 2003 at 11:18 PM EST (Pad 17-B) and landed on Mars on January 24, 2004.

Both were launched from the Delta II rocket which was also responsible for launching all Mars related missions: Mars Global Surveyor in 1996, Mars Pathfinder in 1996, Mars Climate Orbiter in 1998, Mars Polar Lander in 1999, Mars Odyssey in 2001, and Mars Phoenix in 2007.

The tall object on the probe is the "pan-cam" and is designed to be the height of an "average" human so the proper perspective can be achieved. Additionally, the wing like structure are the solar panels, used to recharge the batteries. While the mission was only expected to last a few months, both probes are still operating!

The image above shows a self portrait by the Spirit rover.

The purpose of the rovers are to examine closely the chemical makeup of the rocks and soil. Special instruments on the rovers include spectrometers and a rock cutting tools.

While the data is still being collected and analyzed, the results are wonderful - water did exist at some point on the Martian surface.


Week in Review slideshow of MER discoveries:

2004:
February 29 to March 5 March 6 to March 19 March 13 to March 19
March 20 to March 26 March 27 to April 2 April 3 to April 9
April 10 to April 16 April 24 to April 30 May 1 to May 7
May 8 to May 14 May 15 to May 21 May 22 to May 28
May 29 to June 4 June 5 to June 11 June 12 to June 18
June 19 to June 25 June 26 to July 2 July 3 to July 9
July 10 to July 16 July 17 to July 23 July 24 to July 30
July 31 to August 6 August 7 to August 20 August 21 to August 27
August 28 to September 3 September 4 to October 8 October 9 to November 5
November 6 to December 12 December 12 to January 3  

2005:
January 3 to January 31 February 1 to February 28 March 1 to March 31
April 1 to May 27 May 28 to June 30 July 1 to July 31
August 1 to August 31 September 1 to September 30 October 1 to October 31

One Year Anniversary Slide Show


Some of the equipment used on the rovers are:

Alpha-Particle X-Ray Spectrometer (from the MER Datasheets):

The Athena Alpha Particle X-ray Spectrometer works by exposing martian materials to energetic alpha particles and x rays from a radioactive 244Cm source, and then measuring the energy spectra of backscattered alphas and emitted x rays. The instrument is conceptually similar to the APXS instrument that flew on the Mars Pathfinder mission. However, there are several differences that improve the instrumentís reliability and performance. Unlike the Pathfinder APXS, the Athena APXS does not have a proton mode. The proton mode has been dropped because recent increases in the spectral resolution and sensitivity of the x-ray mode have made it unnecessary. Significant modifications have also been made to the instrument to reduce the CO2-induced background that was observed on Pathfinder, to improve x-ray spectral resolution, and to decrease susceptibility to electromagnetic interference. In addition, the Athena APXS will undergo extensive preflight calibration under Mars-ambient conditions, and will have two onboard reference targets for postlanding calibration on Mars.

The APXS instrument consists of a sensor head mounted on the roverís Instrument Deployment Device, and electronics mounted in the roverís Warm Electronics Box.

The sensor head contains six 244Cm alpha radioactive sources with a total source strength of about 30 mCi. The sources are each covered with 3-μm aluminum foils that reduce the energy of emitted alpha particles from the initial value of 5.8 MeV to about 5.2 MeV. At this energy, the alpha particle scattering cross section of carbon is significantly reduced. The reduction is accompanied by a slight degradation of the alpha spectral resolution caused by broadening of the excitation spectrum, but the net result is a significant suppression of atmospheric background in the alpha spectra. Collimators in front of the sources define the instrumentís field of view, which is about 38 mm in diameter at the nominal working distance of 29 mm.

Surrounding the sources are six thin alpha detectors. The FWHM for the alpha mode of a 244Cm peak at 5.8 MeV is less than 100 keV. Interior to the ring of sources is a single high-resolution silicon drift x-ray detector with a 5-μm beryllium entrance window. The FWHM of this detector at 6.4 keV is about 160 eV, compared to 260 eV for the Pathfinder APXS. The noise level in the x-ray mode will be less than 600 eV at temperatures below ñ30∞C, and the efficiency at the 1.24 keV line of Mg will be at least 20%.

Preamplifiers for both detector channels and a circuit to generate detector bias voltages are also mounted on the sensor head, significantly reducing the instrumentís susceptibility to electromagnetic interference.

The entrance to the detector head is normally protected from martian dust and other potential contaminants by a pair of doors. These doors swing inward and lock open when the sensor head is pressed against a target or other hard surface. They can be closed again by actuation of a release mechanism. The inner surfaces of the doors provide a calibration reference surface for the instrument. The sensor head can also, if desired, be brought into contact with the magnetite rich calibration target designed for the Mˆssbauer spectrometer.

Signals from both detector channels are processed by electronics mounted in the rover WEB. Alpha signals from charge-sensitive preamplifiers ñand similarly-x ray signals from a customized voltage-sensitive preamplifiers in the sensor head ñare further amplified and filtered (semi-Gaussian pulse shapes) and then routed to peak detectors, a multiplexer, and into a 16-bit A/D converter for digitization. Signals from comparators that trigger if signals exceed a preset level initiate a sequence of logic signals necessary for peak detection (sample gate and signal hold) and the conversion process (program interrupt, alpha/x-ray flags). A microcontroller selects the appropriate input to the multiplexer and controls analog-to-digital conversion. The analyzed events are stored in the microprocessor buffer memory, building up alpha- and x ray spectra.

The rover can place the APXS sensor head in contact with rock surfaces or soil surfaces at inclinations within the range of 0 to 90∞. Under normal conditions, it should be possible to position the instrument centerline within 0.4 cm of a target location that has been observed by another IDD instrument.

Proper preflight calibration is essential to analysis of APXS data, so the Athena APXS will undergo an extensive calibration program. All calibration measurements will be made in a chamber filled with a mixture of gases that closely matches the composition of the martian atmosphere, at the appropriate atmospheric density. Calibration measurements will include:

  • spectral ìlibraryî measurements of pure elements and oxides;

  • geochemical standards that span the full range of plausible martian surface compositions;

  • standard targets under a range of atmospheric densities and measurement geometries;

  • standard targets in both natural and powdered form, to investigate texture effects;

  • the APXS flight calibration target;

  • the magnets of the magnet array;

  • several blind certified geochemical reference standards, for independent assessment of the accuracy with which compositions can be measured.

All of these measurements will be made using the flight radiation sources.

The accumulation time for the APXS will typically be at least 10 hours per sample analysis, although significantly shorter durations are possible when only the x-ray mode is used. Most data accumulation will take place during the night when the ambient martian temperature is the lowest, giving the best energy resolution on all spectra. However, it is desirable to break the total accumulation time into several shorter accumulation periods. The APXS can store up to 12 sets of accumulated spectra and can transmit the data to the rover either after each accumulation period, or all sets of spectra at the end of the final accumulation period.

The x-ray mode is sensitive to major elements, such as Mg, Al, Si, K, Ca, and Fe, and to minor elements, including Na, P, S, Cl, Ti, Cr, and Mn. The alpha mode is sensitive to lighter elements, particularly C and O. The depth of analysis varies with atomic number, ranging from approximately 10 to 20 micrometers for sodium, to approximately 50 to 100 micrometers for iron. The detection limit is typically 0.5 to 1 weight percent, depending on the element. The APXS is insensitive to small variations of the geometry of the sample surface because all major and minor elements are determined, and can be summed to 100 weight percent.

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Microscopic Imager (from the MER Datasheets):

The Athena Microscopic Imager (MI) is a high-resolution imaging system mounted on the IDD. The camera body is identical to the ones used by Pancam, so the field of view is 1024 x 1024 pixels in size and the instrument has the same basic radiometric performance characteristics as Pancam. There is a single broad-band filter, so imaging with the Microscopic Imager is monochromatic.

The MI optics employ a simple, fixed focus design at f/15 that provides 3 mm depth-of-field at 30µm/pixel sampling. The field of view is therefore 3131 mm at the working distance. The focal length is 20 mm, and the working distance is 63 mm from the front of the lens barrel to the object plane. The object-to-image distance is 100 mm. Preflight geometric calibration will thoroughly characterize the geometric distortion of the system.

The spectral bandpass of the MI optical system is 400-680 nm. At best focus, the modulation transfer function of the optics is at least 0.35 at 30 lp/mm over this bandpass. Radiometric calibration of the Microscopic Imager will be performed with a relative (pixel-to-pixel) accuracy of 5%, and an absolute accuracy of 20%. Calibration measurements will be obtained every 10 nm over the instrument's full spectral bandpass. The MI signal to noise ratio will be at least 100 for exposures of 20% full well over the spectral bandpass and within the calibrated operating temperature range (-55 to +5∫ C).

No onboard radiometric calibration target is provided for inflight calibration of the MI. It is likely that the MI will be able to view the Compositional Calibration Target, and that this target will provide fiducial marks that can be use to perform a focus check. The MI will be able to acquire unfocussed images of the martian sky, providing flat fields.

The MI will be mounted on the Instrument Deployment Device (IDD), allowing it to be placed against surfaces that can also be examined by the other Athena instruments. The IDD will have a minimum controllable motion along a science target's surface normal vector of 2}1 mm RMS, allowing it to image a rough surface in a sequence of images. After placing the MI in position for imaging, the motion of the IDD damps down to an amplitude of less than 30 microns (i.e., less than one MI pixel) within 15 seconds. Whenever the MI is not in use, the MI optics are protected from contamination by a transparent cover. Preflight calibration imaging will establish the transmission properties of the cover. The cover is opened only for MI imaging sequences. A contact sensor attached to the MI will be used to detect rock and other hard surfaces, to help ensure accurate positioning and protect the MI from accidental damage.

The MI acquires images using only solar or skylight illumination of the target surface. Stereoscopic observations and mosaics can be obtained by moving the MI between successive frames. Stereo images and images taken at various distances from the target will be used to derive the 3-dimensional character of the target surface. Optical sections will also be combined to produce an image of the target that is well-focused across the entire frame.

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Mini Thermal Emission Spectrometer (from the MER Datasheets):

Mini-TES is a Michelson interferometer that provides a spectral resolution of 10 cm-1 over the wavelength range from 5-29 µm (2000 - 345 cm-1). The instrument is mounted inside the rover, and views the terrain around the rover by using the PMA as a periscope. A scan mirror assembly atop the PMA reflects radiation down through the PMA and into the telescope and interferometer. The scan mirror assembly allows Mini-TES to provide spectral image cubes over a 360∞ range in azimuth and from 50∞ to +30∞ in elevation. The scan mirror assembly also provides a view of internal and external, full-aperture calibration targets. The elevation mirror can be slewed to a stowed position in which a cover blocks the Mini-TES aperture in the PMA, protecting the optics from dust accumulation.

Mini-TES has two spatial resolution modes. A solenoid-activated field stop can be removed from the optical path to provide an IFOV of 20 mrad, or inserted to provide an IFOV of 8 mrad. Baffles in the PMA define the stray energy field of view and are designed to minimize stray energy from outside the 20 mrad IFOV from entering the interferometer. The inside of the PMA is designed to minimize the stray background energy from the PMA itself.

During data acquisition, the PMAs elevation mirror and azimuth actuator are sequenced to generate a raster image of the scene. The scan mirror assembly can also be commanded to allow Mini-TES to view the internal and external calibration targets regularly in order
to maintain instrument calibration during an image acquisition. The elevation and azimuth servos move and settle to each commanded position ±1 mrad. Elevation steps of up to 20 mrad in size take place within the 200 msec retrace period of the Mini-TES interferometer, while azimuth steps may take as long as 1 second. Slews to the calibration targets take significantly longer.

The Mini-TES telescope at the base of the PMA is a reflecting Cassegrain configuration with a mirror diameter of 6.35 cm, a focal ratio of f/12, and an intermediate field stop that feeds an approximately collimated beam into the Mini-TES interferometer. The 6.35-cm telescope diameter defines the minimum size of the Mini-TES beam; the beam diverges further at an angle of either 8 or 20 mrad, depending on the resolution mode chosen. The optical design provides for more than 85% of the encircled energy to be contained in an
area equal to a single IFOV, 98% within an area equal to 2 ◊ 2 IFOV, and 99.8% within an area equal to 3 ◊ 3 IFOV. Focus is maintained from 2 meters to infinity, with a blur of no more than 15% of an IFOV at infinity focus.

The Mini-TES Michelson interferometer uses the same flexure-mounted linear motor mechanism and drive electronics as the Mars Observer (MO)/Mars Global Surveyor (MGS) TES instrument. The system uses a 980-nm interferometer to generate interference fringes that control the linear drive servo and time the acquisition of the IR spectrometer data samples. The design is simplified from the TES by combining the
infrared and visible counting interferometers into one interferometer at one end of the motor drive and replacing neon bulbs with redundant laser diodes. Double-sided interferograms at a spectral resolution of 10 cm-1 are obtained with a mirror travel distance of 0.55 mm in 1.8 sec. A voltage ramp is used to drive the mirror at a fixed velocity, and position feedback is obtained from a linear voltage displacement transducer. Optical switches sense beginning of scan and synchronize the interferometer with the elevation and azimuth drive motors.

Mini-TES uses a single uncooled deuterated triglycine sulfate pyroelectric detector sized to define the instruments 20-mrad IFOV. The IFOV, dwell time, and interferometer scan rate have been selected to produce frequencies in the range of 15 to 120 Hz which is
the range over which minimum noise equivalent spectral radiance (NESR) can be achieved. The detector provides the necessary performance over a temperature range from 10 to +20∞C and with reduced performance from 40 to +35∞C.

The NESR of the Mini-TES for a single spectral accumulation interval at 10 µm observing a scene at 270 K and 20 mrad will be <1.25 ◊ 10-8 W cm-2 sec-1 sr-1, corresponding to a signal-to-noise ratio (SNR) of at least 450 for co-addition of two observations. Radiometric calibration of Mini-TES over its full spectral range will be performed with an absolute accuracy of 5% or better and a relative precision (pixel-to -pixel) of 2% or better, viewing a 270 K blackbody. The internal calibration target is located inside the head of the PMA, and the external target is located on the deck of the rover. Both targets have V-grooved surfaces and are coated with high emissivity paint. Temperature sensors affixed to both targets have an absolute accuracy of ±0.2∞C and a precision of ±0.1∞C.

The instruments electronics are based on the electronics of the MO/MGS TES. A 14.515 MHz internally-generated clock signal provides the control timing for the interferometer motor controller and synchronizes the scan timing and data collection events with the
rover computer. Detection of start of scan by the optical switches also signals to the rover computer that data collection has begun. This signal triggers an internal timer that initiates retrace of the interferometer mirror after 1.8 seconds. Signals from the detector
are fed through a pre-amplifier, variable gain post-amplifiers for each field of view, an analog multiplexer, a 16-bit A/D converter, and into an output buffer.

Mini-TES begins collecting data at the application of power. The instrument acquires data in a cyclic fashion, with a period of two seconds corresponding to the Michelson mirror scan followed by its retrace. Spectral integration is coordinated with the PMA elevation and azimuth drive mechanisms using the rover computer. On each two-second period (known as one ICK), the hardware fills up the Mini-TES data buffer with header data, interferogram data from the selected spectrometer field of view, and the telemetry data.

Mini-TES flight software controls the transfer of the data from the Mini-TES data buffer to the rover CPU memory. Once the Mini-TES data is available in the rover memory, the flight software performs a Fourier transform on the interferogram in order to generate a spectrum. It then performs data aggregation in order to reduce the total volume of data to be downlinked. Separate programmable data aggregation modes in the spatial domain (averaging spectra from consecutive ICKs) or in the spectral domain (averaging data from contiguous spectral points) are available. Data volume is further reduced via lossless compression using a Rice algorithm. Compressed data then undergoes final formatting, packetization, and transfer of the packets to rover data storage for downlink.

The rover computer issues commands to PMA motor driver circuitry in order to synchronize the mirror movements to the Mini-TES data acquisition. Direct commands from the rover computer control instrument power and selectable gain state, field of view, motor on/off, laser heater on/off, redundant start-of-scan optical switches, and redundant laser diodes.

Mini-TES operates primarily during mid-day (10 a.m. to 3 p.m. local time) to obtain high-quality spectral measurements of emitted infrared energy. Nighttime observations may be obtained to measure surface and atmospheric temperatures of the full diurnal cycle for thermophysical and boundary layer studies.

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Mossbauer Spectrometer (from the MER Datasheets):

The Athena Mˆssbauer spectrometer uses a vibrationally-modulated 57Co source to illuminate target materials. Backscattered gamma signals are binned according to the source velocity, revealing hyperfine splitting of 57Fe nuclear levels that provides mineralogical information about the target. The main parts of the instrument are the Mˆssbauer drive that moves the 57Co source with a well-known velocity, the γ- and x-ray detectors that detect the backscattered radiation, the
microcontroller unit, the 57Co/Rh Mˆssbauer source, and the radiation collimator and shielding.

The spectrometer is split into the sensor head on the roverís Instrument Deployment Device (IDD), and the electronics in the warm electronics box (WEB). The sensor head carries the Mˆssbauer drive with the analog part of the drive control unit, the 57Co/Rh Mˆssbauer source, the radiation collimator and shielding, the four PIN- diode detector channels including pulse amplifiers, and one reference detector channel to monitor the velocity of the drive using a weak
57Co source and a well known Mˆssbauer reference absorber in transmission geometry.

The WEB electronics consist of the microcontroller and memories for data acquisition and temporary storage. An extra FPGA logic unit provides several functions for internal communication, generates the velocity signal for the drive, and contains fast pulse counters for
the detector signals. The WEB electronics also contain voltage supply regulators and detector bias voltage generators.

The analog signals of the five detector channels are analyzed by discriminators for 14.4 keV and 6.4 keV peaks. Upper and lower threshold values of the discriminators are generated by digital to
analog converters (DACs). These values can be changed automatically to follow the temperature drift of the amplifiers. Digital signals from the discriminators are sent to the velocitysynchronized counters whenever a detected pulse is within the specified range. Mˆssbauer spectra for the two different energies of 6.4 keV and 14.41 keV are sampled separately.

The Mˆssbauer spectrometer has its own internal microcontroller, so that it can collect data independently of the rover computer. Instrument parameters are stored in a fault-tolerant fashion in 3 separate FRAMs and default values for these parameters are taken from ROM in case of an error. Every 60 minutes during a measurement, data is stored into the EEPROM. In case of a failure of the power supply, after restart of the instrument the data acquisition will continue with this data. Each Mˆssbauer spectrum consists of 512 ◊ 3-byte integers. The pulses from the 4 counters are added by hardware. Normally there is one spectrum for each detector. The spectra are sampled into an SRAM of 128 Kbytes size.

Measurements are made by placing the instrument directly against a rock or soil sample. Physical contact is required to provide an optimal measurement distance and to minimize possible microphonics noise on the velocity-modulated energy of the emitted γ rays. The mechanical construction of the IDD and the interface limit vibration-induced velocity noise at the sensor head to less than 0.1 mm/s. A contact plate is mounted at the front part of the sensor head, assuring an optimal distance from the sensor head to the sample of about 9 to 10 mm. A heavy metal collimator in front of the source provides an irradiated spot of nominally 15 mm (up to 20 mm, depending on actual sample distance and shape) in diameter on the surface of the sample. The IDD can position the instrument with an accuracy of 0.4 cm or better with respect to the position observed by other IDD-mounted instruments. The average depth of sampling by Mˆssbauer data is about 200 to 300 μm.

Mˆssbauer parameters are temperature dependent. Especially for small particles exhibiting superparamagnetic behavior (e.g., nanophase Fe oxides), the Mˆssbauer spectrum may change drastically with temperature. The observation of such changes will help in determining the nature of the iron-bearing phases. Therefore Mˆssbauer measurements will be performed over a range of diurnal temperatures spanning both the daytime maxima and the nighttime minima.

One Mˆssbauer measurement takes approximately 12 hours, depending on the phases present in the sample and the total iron content. The temperature variation for one spectral accumulation interval will not be larger than about ±10∞C. When larger variations occur, spectra for different temperature ranges are stored separately, resulting in an increase in the total data volume (depending on the number of temperature intervals required), and a decrease of statistical quality
for the individual subspectra.

In parallel with the measurements of samples, calibration spectra will be taken using the reference channel implemented in the instrument. A calibration target containing a thin slab of magnetite-rich rock will also be included on the rover where it can be viewed directly by the
instrument immediately after landing, as well as later in the mission if necessary.

The performance of the Mˆssbauer Spectrometer can be defined by measurements made in transmission geometry with a Mˆssbauer source in front of the instrument at a distance of 5 cm, and in a backscattering geometry with the source internal to the instrument in its flight configuration. Instrument performance requirements for such purposes are specified for a Mˆssbauer source strength of 100 mCi for the backscattering mode, 10ñ20 mCi for transmission mode, an integration time of 10 minutes for the energy spectra (backscattering and transmission), and an integration time of 10 hours for the Mˆssbauer backscattering spectrum.

(1) Specifications for the energy spectra taken in transmission mode (see Figure 1) at a temperature of +20 (±1)∞C are:

  • noise level: The intensity at (A) (channel 11) will not exceed 20.000 (±1000) counts;

  • at (B) (ìvalleyî, channel 15), the intensity will be less than 8900 (±500) counts; and

  • the peak-to-valley ratio (ratio of intensities at (C) (channel 19) and (B)) will be equal to
    or larger than 1.5.

(2) Specifications for the energy spectra taken in backscattering mode (see Figure 2) at a temperature of +20 (±1)∞C are:

  • noise level: The intensity at (A) (channel 18) will not exceed (50 ±10) counts;

  • at (B) (channel 36) the intensity will be less than 23 ±5 counts;

  • within the energy range channel 25 to channel 50 the intensity will be between 2 and 25 counts; and

  • at (C) (channel 145) the tantalum X-ray line generated in the collimator will be visible; the intensity will be 18 ±4 counts.

(3) Specifications for the Mossbauer spectra taken in backscattering mode (bottom figure) on its magnetite-rich calibration target at a temperature of +20 (+/-1) degrees Celsius are that:

  • the peak/background ratio will not be less than 1.11, as shown in Figure 3; for a source activity between 80 and 120 mCi; and

  • the magnetite signal will be visible with a peak/background ratio of not less than 1.005.

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Pancam (from the MER Datasheets):

Pancam uses 1024◊2048 pixel Mitel CCD array detectors developed for the MER Project. The arrays are operated in frame transfer mode, with one 1024◊1024-pixel region constituting the active imaging area and the another adjacent 1024◊1024 region serving as a frame transfer buffer. The frame transfer buffer has an opaque cover that prevents >99% of light at all wavelengths from 400 to 1100 nm from being detected by this region of the CCD. The pixels are continuous, and the pitch is 12 μm in both directions. The arrays are capable of exposure times from 0 msec (to characterize the ìreadout smearî signal acquired during the ~5 msec required to transfer the image to the
frame transfer buffer) to 30 sec. Under expected operating conditions, the arrays have at least 150,000 electrons of full-well depth, and a read noise of less than 50 electrons. Dark current varies with temperature; it is negligible at -55∞C and is <1200 electrons/sec
at 0∞C. Analog to digital converters provide a digital output with 12-bit encoding, and SNR > 200 at all signal levels above 20% of full scale. The detector response has a linearity > 99% for signals between 10% to 90% of full well.

Each array is combined with optics and a small filter wheel to form one eye of a multispectral, stereoscopic imaging system. The optics for both cameras consist of identical 3-element symmetrical lenses with an effective focal length of 38 mm and a focal ratio of f/20, yielding an IFOV of 0.28 mrad/pixel and a square FOV of 16.8∞◊16.8∞ per eye. The optics and filters are protected from direct exposure to the martian environment by a sapphire window at the front of the optics barrel. The optical design provides for more than 90% of the encircled energy to be contained in an area equal to 3◊3 IFOVs, and 99% in an area equal to 5◊5 IFOVs, across the entire range of spectral responsivity of the instrument and over the required operating temperature range for performance of Pancam within specifications (-55∞C to 0∞C). The optical design allows Pancam to maintain optimal focus from infinity to within about 1.5 meters of the cameras. At ranges closer than 1.5 meters, Pancam images suffer from some defocus blur. For example, at a range of 80 cm (the approximate distance from the Pancam calibration target), the defocus blur is about 10 pixels.

Each filter wheel has eight positions, allowing multispectral sky imaging and surface mineralogic studies in the 400-1100 nm wavelength region. The left wheel contains one clear (empty) position. The remaining filter wheel positions are filled with narrowband interference filters that are circular and 10 mm in diameter, and that have the central wavelengths and bandpasses listed in Table 2.1.2-1. One filter on each eye has an ND5.0 coating to allow direct imaging of the Sun at two wavelengths.

Radiometric calibration of both Pancam cameras will be performed with an absolute accuracy of 7% or better and a relative precision (pixel-to-pixel) of 1% or better. Calibration will be achieved using a combination of preflight calibration data and inflight images of a Pancam calibration target carried by the rover. The Pancam calibration target is placed within unobstructed view of both camera heads and will be fully illuminated by the Sun between at least 10:00 AM and 2:00 PM local solar time for nominal rover orientations. The target has three gray regions of variable reflectivity (approximately 20%, 40%, and 60%) and four colored regions (peak reflectance in the blue, green, red, and near-IR) for colorimetric calibration. It includes a vertical post that will cast a shadow simultaneously across all three gray surfaces at some time within the 10:00 AM to 2:00 PM nominal operating range. The calibration target is large enough that defocus
blur will not produce significant degradation of the calibration images.

The two Pancam eyes are mounted on a mast on the rover deck. The mast is referred to as the Pancam Mast Assembly (PMA), and also includes several key components for the Mini-TES. The PMA is erected to the vertical position by a deployment actuator at its base. The cameras are located on a "camera barî with a boresight 180∞ from the Mini-TES boresight. The rover navigation cameras (Navcams) are also located on this same camera bar, and point in the same direction as Pancam. The boresight of the Pancam cameras is approximately 1.3 m above the martian surface with the PMA in the deployed position. The cameras are moved together by ±90∞ in elevation using a geared brush
motor on the camera bar. The entire PMA head, including the cameras, can be rotated 360∞ in azimuth by a geared brush motor assembly. A separate geared brush motor provides elevation actuation for the Mini-TES elevation mirror assembly. Hard stops are provided for all actuation axes.

The two Pancam eyes are separated by 30 cm horizontally and have a 1∞ toe-in. This separation and toe-in provide an adequate convergence distance for scientifically useful stereo topographic and ranging solutions to be obtained from the near-field (5-10 m) to
approximately 100 m from the rover. Pointing control is <2∞ in azimuth and <1∞ in elevation. Pointing knowledge relative to the hardstops is 0.1∞ over the entire range of motion of Pancam.

Pancam will operate primarily during the daytime to obtain high-quality measurements of sunlight reflected off rock and soil surfaces and airborne dust particles, as well as direct solar images using the two ND filters. Twilight or nighttime sky or astronomical object imaging may be possible but has not been committed to by the Project. The required
operating temperature range for performance of Pancam within specifications is -55∞C to 0∞C.

Pancam will be commanded by and will return digital data directly to the rover computer. The computer provides the capability to perform a limited set of image processing tasks
on Pancam data prior to transmission. These tasks include (1) bias and dark current subtraction, (2) electronic shutter effect correction, (3) bad pixel replacement, (4) rudimentary automatic exposure control capability to maximize the SNR of downlinked data while preventing data saturation, (5) image subsampling and subframing, and (6)
image compression using a JPL-developed wavelet compression algorithm called ICER.

Pancam telemetry is collected by the rover computer and downlinked according to an overall priority queue scheme agreed upon in advance by the MER Science Operations Working Group. Image data are packetized, with each packet containing sufficient information to allow receipt in any order and to allow incremental image reconstruction
even in the event of typical transmission errors and packet losses.

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Rock Abrasion Tool (from the MER Datasheets):

The Rock Abrasion Tool (RAT) will be used to penetrate through dust and surface alteration that might be present on rocks, exposing materials more likely to preserve evidence of environmental
conditions at the time of their formation. The fresh surfaces exposed can then be characterized by all of the Athena instruments. The RAT is a diamond-tipped grinding tool capable of removing a cylindrical area 4.5 cm in diameter and at least 0.5 cm deep from the outer surface of a rock. This operation takes about 2 hours for a dense basalt.

The RAT has a total of three actuators (see figure). One causes each of two grinding wheels to rotate at high speeds. Each of these grinding wheels has two teeth, which cut out a circular area associated with each grinding head as the head rotates. A second actuator causes the two grinding wheels to revolve around one another at a much slower rate, sweeping the two circular cutting areas around the full 4.5-cm diameter cutting region. Finally, a third ìz-axisî actuator translates the entire cutting head toward the rock, causing it to penetrate to the commanded depth.

In order to grind a rock, the IDD places the RAT directly against it. Contact is made on two small spikes external to the grinding heads, and a ring surrounding the heads can adjust in two orthogonal axes to the orientation of the rock surface. Once pressed firmly against the rock by the IDD, all further actuations take place within the RAT itself. Rotation and revolution of the grinding wheels is initiated, and they are slowly translated toward the rock surface by the z-axis actuator until contact is made. Encoders monitor penetration progress, and allow closed-loopcontrol of the grinding process. A dust skirt around the cutting surfaces helps to prevent release of dust that might contaminate instruments.

The RAT is designed to preserve petrologic textures of the prepared rock surfaces as fully as possible, so that they can be viewed effectively using the MI. The grinding process is slow enough that no measurable modification of rock chemistry or mineralogy by frictional heating is anticipated. The grinding wheels are designed so that contamination of the exposed surface by cuttings from the rock (and previous rocks) is minimized. Grinding wheel materials are selected
so that there should be no detectable contamination of rock surfaces due to wear of the grinding heads themselves.

During the operation of the RAT, the rover will monitor currents, temperatures, and encoder readouts for all three RAT actuators. These data can be used to infer information about the strength properties of the rocks that have undergone grinding. A pre-flight test program is planned to establish some of the relationships among these parameters and rock strength, but this program will be limited in scope. Further post-launch testing with an engineering model or flight spare RAT is possible.

 

Since the mission is still on-going, up to date information will be available from the Mars Exploration Rovers website.

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